ZGM is a large glycoprotein tumor marker demonstrable immunohistologically in colo-rectal and other cancers. Smaller molecules having ZGM imunoreactivity are being isolated from the plasma of patients with colo-rectal adenocarcinomas. A molecule will be selected for use in measuring circulating ZGM by a more specific and sensitive assay than that used previously employing a ZGM isolated from malignant tumor tissue. Small molecule tumor tissue ZGM produced by degrading large molecule tumor tissue ZGM by insolubilized (solid phase) neuraminidase and trypsin is being studied. Monoclonal antibodies and xenogeneic antisera to small molecule ZGM obtained from plasma and tumor tissue is being produced for potential clinical application in a plasma assay.